The present invention relates to an improvement in a method for lining internal surfaces of pipelines for various pipings, such as water pipes and gas pipes, in which a plurality of branched pipelines branch from a main pipeline. Moreover, the present invention relates particularly to a shaping method for lining such internal surfaces.
In the past, a method involving blowing a coating composition into a pipeline with the aid of an air current to effect lining has been widely used for renewal of water pipes and gas pipes, as disclosed, for example, in Japanese Patent Laid-open Publication No. 2(1990)-68177.
According to the aforesaid technique, if the viscosity of the coating composition and air speed are properly selected and a coating having an excellent run characteristics is used, excellent lining can be carried out.
However, this method involves a problem which is difficult to solve in that the film thickness of the lining on the back surface of an elbow tends to become thin.
This problem occurs due to the fact that when an air current impinges upon the back of an elbow and then changes its direction, the action for forcibly spreading a film is quite strong. Thus, it is difficult to secure a film thickness of practical requirements under the air flow velocity required for an air flow method.
This method sometimes involves a further problem in that if coating conditions such as flow velocity are mistaken, the coated film becomes too thick or too thin.
As methods for solving these problems, a method has been carried out to smooth the coated film and correct its thickness through the use of a shaping pig before the coating is cured (For example, Japanese Patent Laid-open Publication Nos. 62(1987)-266178 and 63(1988)-274474).
However, the pig used in the conventional method is so high in density that when it is strongly compressed, the force for pressing the inner wall of the pipe becomes excessively strong and scrapes off the coated film. Therefore, a ball-like pig, which is somewhat smaller than, or one-size smaller than, the inside diameter of the pipe has been used. Accordingly, in this method, the pig is of the size adjusted by the minimum size of pipes used in the piping. Therefore, where pipe sizes are different, there is a problem in that a sufficient effect cannot be obtained for pipe portions whose size is large. Moreover, since the pig is moved from the side of a main pipeline whose size is large to the side of a branched pipeline whose size is small, in branched portions, the pig does not enter the branched pipeline but tends to move straight ahead along a main pipeline portion.
As measures for solving this problem, Japanese Patent Laid-open Publication No. 1(1989)-304086 proposes a method in which a pig is introduced into a branched pipeline with the aid of air also from the side opposite to a main pipeline (See FIG. 4, numeral 1 denotes a main pipe, and 1A denotes a branched pipe).
However, also in this case, the pig is moved from a main pipeline toward a branched pipeline. At the branched portion, even if a pig is pushed by an air current from the side opposite to the main pipeline, the pig as well as coatings accumulated in front of the pig do not enter the branched pipeline but tend to be transferred to the main pipeline on the opposite side. Since the pig is pushed by the air current from the side opposite to the main pipeline, the pig transferred to the opposite side is pushed back after all and moves to the branched pipeline. However, the coating having been pushed by the pig remains thick and hardens within the main pipeline. Thus, the object of shaping inner surfaces is not attained.
Furthermore, Japanese Patent Laid-open Publication No. 1(1989)-304086 discloses, instead of shaping a coated film subjected to lining by an air current method, a method for lining in which a coating is placed frontwardly of a pig, and the coating is pushed by air rearwardly of the pig. In this method, where the size of a branched pipeline is smaller than that of a main pipeline, the outside diameter of the pig is contracted due to compression.
However, the characteristics of the pig is not further defined, and therefore, there remains a question as to whether the necessary thickness of the coating is formed by a pig of reduced diameter.